The present invention relates to a percussion drill such as a rock drill, and more particularly, an apparatus for withdrawing a drilling rod of a rock drill and the like.
In spite of the fact that average drilling and rod recovering time in drilling of a hole of 3 inches (75 mm) diameter and 39 feet (12 m) depth has been reduced to approximately 15 minutes at places where the lithology is relatively uniform and good, there is also known occasions where only one hole can be drilled in a day. Such poor efficiency is usually caused by occurence of a jammed or clogged drill hole.
Accordingly, it is an object of the present invention to provide a percussion device for a tool such as a rock drill, said device contributing to improve the working efficiency of drilling by withdrawing a drilling rod without the influence of jamming.
It is another object of the present invention to provide a percussion device for a tool such as a rock drill, which device eliminates the need of means for preventing jamming of a drilling machine or simplifies said means and can lighten the mental load of operators.
These and other objects are obtained in a percussion tool having a machine housing, a main piston reciprocated within the machine housing by fluid pressure, and an anvil element exerted with a first impact thereon by the forward movement of the main piston, and adapted to exert a second impact on the anvil element in the direction opposite to that of the first impact, a reversal percussion device, for the percussion tool comprising a source of pressurized fluid for supplying pressurized fluid, a buffer chamber receiving the pressurized fluid, a machine housing constituting a portion of the buffer chamber, and a secondary piston constituting a portion of the buffer chamber and sliding to allow the volume of the buffer chamber to be varied, the secondary piston having a piston surface limiting the axial portion of the buffer chamber near the main piston.
In the present invention, jammed rod withdrawal is made possible by an impacting piston imparting impacts on a shank rod simultaneously with application of a conventional mechanical pulling force on the rock drill. Impact energy transmitted to the shank rod by the impacting piston is recovered so that impact pressure is averaged over a certain time by a secondary piston and an accumulator, and following retraction of the impacting piston, the secondary piston and the shank rod is instantaneously pushed back in the reverse direction.
This means that impact pulses in the directions in which a working tool is compressed and pulled, are alternately exerted on a working tool such as a shank rod, a rod and a bit. Therefore, rod withdrawal which was so far difficult can be easily performed in a short time. This permits substantial reduction of working time.